1. Field of the Invention
These inventions relate to buoyant-slat automatic pool cover systems and tuning techniques harnessing buoyancy forces for optimizing and overcoming inherent functional deficiencies in such systems.
2. Description of the Prior Art
Automatic pool cover systems utilizing interconnected rigid buoyant slats described in U.S. Pat. No. 3,613,126, R. Granderath, which roll up on a submerged or elevated drum are popular in Europe. Such buoyant slat pool cover systems for non-rectangular shaped pools have covers which emerge from covered troughs below the pool bottom in the center of a pool and extend to the pool ends. [See EPO 0369038 A1 & B1, R. Granderath and DE 19807576 A1, K. Frey.] Descriptions of typical buoyant slats for such pool cover systems are described in U.S. Pat. No. 4,577,352, Gautheron, and in. U.S. Pat. No. 5,732,846, Helge, Hans-Heinz (See also DE 4101727 and EP0 225862 A1.)
U.S. Pat. No. 4,411,031 Stolar describes a pool cover system similar to Granderath where, instead of rigid, hinged buoyant-slats, various floating sheet materials such as a polyethylene poly-bubble, or a laminate of vinyl sheeting and foamed substrate, are floated onto the surface of the pool water. Similar to Granderath, extension of Stolar type covers across pools is reliant on buoyant and gravitational forces.
The disadvantage of buoyant pool cover systems utilizing passive buoyancy or gravity forces for propelling or extending the cover components across a pool surface is that the passive forces are always present, and must be dealt with when the cover is stored fully wound up around the cover drum underneath the pool surface, when the cover unwinds from around the drum on extension, and when the cover winds up around the drum on retraction.
Pool cover systems that use buoyancy to propel floating covers across the pool, most typically wind the cover onto roller drums positioned below the water surface. When the cover is retracted from the pool surface and fully wound up onto the cover drum, the upper extremity or front/leading edge of the cover typically is at least two inches below the water surface of the pool. In some cases, the wound up cover and drum are located in a trough next to the pool. In other cases, the cover and drum may be located in an enclosure near the bottom of the pool, or in a special hidden trough compartment underneath the pool floor aesthetically hiding the cover and roller drum. In all cases, the cover drum mechanism is usually located or covered so that that swimmers and the mechanism cannot interfere with each other.
When a buoyant cover is wound up around the cover drum, underwater buoyancy forces act on both sides of the wound up cover with the cover drum acting as a pivot tending to turn in the direction on the side with the greater force. Accordingly, when the cover is fully retracted, the cover drum must be held stationary. An even more perplexing problem is that buoyancy forces tend to unwind the spirally wound up layers of the cover from around the cover drum, particularly in instances where the tongue or front portion of the cover has less volume (is less buoyant) than the main body cover. Typically, the front end of the cover is not secured when the cover is fully wound up in the retracted storage position. Accordingly, when the outer cover layer on the winding side of the cover drum is more buoyant than the outer cover layer on the extending side of the cover drum, the imbalance of buoyancy between the winding side and extension side with the cover drum held stationary, will pull the front portion of the cover around the wound cover layers in the winding direction, successively until the buoyancy forces on the respective sides (layers) of the cover roll balance (reach an equilibrium). Such passive unwinding or loosening of the retracted cover in the cover drum trough increases the cover roll radius leading to jams when that radius reaches or exceeds a design parameter such as a trough wall. Also such loosening effectively precludes limit switch control over cover extension.
The typical buoyant-slat for a pool cover has a transparent upper or top surface and a dark bottom or undersurface (See U.S. Pat. No. 5,732,846, Helge, col. 1, 11 27-34), The slat is a typically an extruded plastic tube with one or more stoppered, air filled longitudinal flotation chambers, having a longitudinal male, prong hook along one side and a longitudinal female prong-receiving channel along its other side [See FIG. 1]. A plurality of slats are interleaved together to form flexible or rollup-able cover. Buoyant pool cover slats are also quite vulnerable to over heating, i.e., heat increases air pressure in the flotation chambers that can compromise the water tightness of the slat. Water convection cools the dark undersides of the slats forming the cover when the cover is deployed on a pool surface.
The coupling between adjacent coupled slats is essentially a loose, longitudinal, bidirectional hinge that is flexible or bendable back and forth around the longitudinal coupling. The longitudinal prong-channel couplings between adjacent slats are typically configured to allow the longitudinal coupling to flex, with reference to a horizontal floating plane of a pool surface, in an underside direction and in a topside direction. The degree of topside and underside flexibility of the coupling between adjacent buoyant slats cover determines both the direction the cover is wound and the minimum diameter of the cover drum. Typically, the longitudinal couplings of the type shown in FIG. 1 allow a 30° topside flex and a 45° underside flex.
Under most circumstances, buoyancy forces keep the longitudinal couplings between adjacent slats in tension underwater until the couplings reach the pool surface. At the pool surface, tensioning due to buoyancy disappears allowing the coupling to unpredictably flex in opposite (topside-underside) directions. Such bidirectional flexing is a problem as the front or leading edge of the buoyant cover, on extension, emerges up through onto the horizontal surface of the pool unguided [See DE19807576 A1, K. Frey.] In particular, a myriad of different factors, e.g., momentum, wind, surface waves, and the like, all can affect the direction the front edge of the cover flexes. For example, the front edge of the cover emerging adjacent an end/side of the pool or other extending cover component, can flop onto the adjacent deck or other extending cover component, rather than the pool surface. In addition to interrupting automatic extension, if not immediately corrected manually, a flop in the wrong direction can lead to extensive damage. In particular, when the front portion of the emerging cover flexes in the topside direction, the cover folds over onto itself as the buoyancy forces accelerate extension of the remainder of the cover onto the pool surface. Folding the cover over exposes the dark undersides of the buoyant slats to the sun. Warmed by the sun, expanding air confined within the hollow slats can quickly compromise the water tightness of the slats.